At this point, Katy Perry and John Mayer don't have a whole lot invested in their relationship: a couple months, some pool party PDA, hanging at a music festival. And in that short time, they've already suffered through one rumored split. Now, there's another sign of imminent doom, specifically, a public spat.

After Katy wrapped up her girl-time with BFF Rihanna at the MTV Video Music Awards on Thursday night, she rendezvoused with John for a romantic dinner and an afterparty.

After chowing down on Italian at hot spot Madeo (and exiting the eatery holding hands), they headed to an Esquire-sponsored House of Hype bash at the Beverly Hills Hotel. All reportedly seemed fine when they arrived (even if they looked a little depressed in the limo), with the popster, still sporting the Elie Saab gown from the VMA red carpet, even receiving a helping hand from her accommodating beau with the dragging hemline of her couture.

But their good mood apparently faded once they were seated inside.

The London Daily Mail says the night took a turn when Perry ordered a bottle of whiskey for their 10-person table. The "air between the couple grew incredibly tense," alleges the tab, and Mayer was spotted "trying to calm" Katy down.

The situation supposedly escalated to the point where they took it to a private area, where it was soon defused (at least one insider says there was no fight at all, and John simply wanted some quiet, one-on-one time with his squeeze).

By the end of the night, Katy, 27, and John, 34, were back to "kissing and cuddling," a spy tells Wonderwall.

Despite the romantic red flags a-flying, the pair have apparently reached an understanding about keeping things casual, which Us Weekly reports they worked out via text and email (oh, those sentimental fools).

Says an insider, "She told him she just wants to have fun."

Adds a Katy confidant to People, "I won't save the date for a wedding."